The copper foil materials used for FPC FPC are mainly divided into calendered copper and electrolytic copper. It is a conductor layer bonded to the covering film insulating material, which is etched into the required patterns through various processing processes. Electrolytic copper foil is obtained by separating acid copper plating solution on bright stainless steel roll to form a uniform copper film, which is continuously peeled and rolled; Calendering copper foil is to use copper ingots or copper blocks with a certain thickness to form the required thickness of copper foil after repeated rolling and annealing.
The atomic structure of copper in the calendering material is irregular layered strong crystal, which is recrystallized after heat treatment, so it is not easy to form cracks, and the bending property of copper foil material is good; The electrolytic copper foil material presents columnar crystal structure in the thickness direction, which is easy to crack and fracture when bending; Similarly, when observing the section of high elongation electrolytic copper foil material after heat treatment and other special processing, although it is still mainly columnar crystal, layered crystal is formed in the copper layer, and it is not easy to break when bending.
After testing, the bending property of rolled copper foil is 4 times that of ordinary electrolytic copper foil, but its price is also expensive. Therefore, for products with low bending requirements (such as key board, module board, 3D static flexible circuit, etc.), high elongation electrolytic copper foil can be used to replace the calendered copper foil. Of course, when the reliability requirements are relatively high (such as slide phone board, folding phone board, etc.), calendered copper foil is preferred.
Most FPC FPC flexible circuit board products have high requirements for bending performance, which leads to the preference of most manufacturers for calendering materials. In fact, there are many blind selection factors. As mentioned above, calendering materials have their own characteristics, and they also have many shortcomings, which should be properly applied.